This request is a resubmission of application #S10-RR08374-01 for funds to purchase a JEOL 1200EXII transmission electron microscope (TEM). This instrument will serve as the primary high resolution microscope within the recently established Structural Biology Imaging Center (SBIC) of the University of Pittsburgh Medical School. The mandate of this facility is to provide access to a full range of electron optical, image analysis, and morphometric methods to all research departments within the medical area. In the year since our previous application, the SBIC has become an integral part of the medical research community, participating in research projects with more than 40 PHS funded research groups within the medical area. The current TEM equipment base consists of a JEOL 100CX and a JEOL 100B. When the SBIC was opened, consultations between the steering committee of the center and the different user groups clearly indicated that the existing electron microscopes were inadequate in terms of both technology and the ability to serve the needs of the research community. Our prediction, at the time of the first grant application, that the availability of microscope time within the facility would reach a premium when the SBIC became fully functional, has indeed been borne out in the past 16 months. Available instrument time has been further compromised by the consistent unreliability of the JEOL 100B. This older microscope has limited functionality and is operable only by "expert" users who understand the quirks of this instrument. It cannot be used by students or by less experienced users. As a result of these problems, we are now limited to the use of our remaining microscope, which cannot and does not provide enough microscope hours to satisfy user demands. In our previous application, we requested funding for a 1200EXII equipped with a goniometer stage and an automontage device. These features were deemed unjustified and, accordingly, have been omitted from the current application. Funds for their purchase have been guaranteed by institutional support. Thus, we have focused our current application to funding for the purchase of the least expensive l20kV instrument available on the market today. The addition of this microscope to the SBIC would enable us to retire the 100B from intensive daily service and to provide high quality instrumentation and sufficient microscope time to our ever- expanding group of users.